A liquid crystal display device of a supertwisted biregringence effect type (the SBE type) have so far been disclosed as a liquid crystal display device capable of providing a high contrast and a large display capacity in multiplex driving at a high duty ratio.
However, a liquid crystal display device this SBE type has a defect that both areas of a displayed image and a background are tinted with a specific color, because a birefringence effect is utilized, and this defect causes the problems of: (1) poor quality of display image: (2) no flexibility to meet the colors requested by users: and (3) difficulty in displaying a full color image.
To solve the above-mentioned tinting problem and provide a clear black-and-white display, the following techniques have been proposed; (1) OMI mode where tinting is prevented in such a way that a product, .DELTA.n.d, of a reflactive anisotropy, .DELTA.n, of a liquid crystal and a liquid crystal layer thickness, d (.mu.m), is set at 0.4 to 0.6 .mu.m, (Appl. Phys. Lett., 50 (1987), pp. 236-238) (2) a double layer cell mode where a double layer cell structure is formed by superposing one liquid crystal cell on another cell containing a reversely twisted structure in a liquid crystal layer in order to prevent tinting by utilizing the another cell as an optical compensator (Nikkei Micro-Device, October, 1987 Issue, pp. 84-88).
However, such as OMI mode as proposed by the above technique (1) has the problems: a high contrast can not be obtained; a displayed image is dark: and tinting can not completely be prevented.
Also, the foregoing double layer cell mode (2) has the problems: a production cost becomes higher and a weight of the device becomes heavier than that of a device composed of a single liquid crystal cell: and because difficulty to make the thicknesses of two liquid crystal cells uniform, the liquid crystal cell does not satisfactorily function as an optical compensator, so that it is difficult to completely prevent tinting.
In addition to the above, the SBE type liquid crystal display device requires an alignment layer providing a high pretilt angle in order to form a stable alignment and to obtain a high contrast. As for a method of forming an alignment layer providing a high pretilt angle, an oblique evaporation-deposition method is known. However, this method has the problems in a mass-productivity and a uniform processability of large area. Recently, there have been proposed several rubbing methods where a high pretilt angle can be provided with an excellent mass-productivity. In this method, however, the possible pretilt angle with a uniform alignment is 25.degree. at most. A liquid crystal display device giving a pretilt angle of less than 25.degree. has not been able to provide any satisfactory contrast in multiplex driving at a high duty ratio.